Conventionally, general microbial treatment systems have an aeration tank with a large capacity, which makes it difficult for factories having smaller installation areas to install the aeration tank. This gives rise to a demand for wastewater treatment methods and wastewater treatment equipment which has a small installation area therefor as well as good performance.
The high-concentration microbial treatment system with use of a submerged membrane suffers a problem of reduction in filtered water amount due to clogging of the submerged membrane as time passes. This gives rise to a demand for a method which makes it possible to effectively clean oil and fat content on the surface of the submerged membrane that causes clogging, even when the clogging of the submerged membrane occurs.
In the case of systems involving only the high-concentration microbial treatment, or in the case of requiring further advanced treatment, treatment of activated carbon adsorption is sometimes added. This causes a problem of higher running cost due to replacement of activated carbon after adsorption of organic matter or the like. This gives rise to a demand for a method which can effectively be cleaned oil and fat content on the surface of the submerged membrane that causes clogging, even when the clogging of the submerged membrane occurs.
As another prior art, JP2004-121962A has disclosed a treatment method and a treatment device with use of nanobubbles.
This prior art utilizes characteristics of nanobubbles such as decrease in buoyancy, increase in surface area, increase in surface activity, generation of local high pressure fields, a surface active property and an antiseptic property which are attained by achievement of electrostatic polarization. More specifically, this prior art has disclosed that the correlation among these characteristics shows a fouling component adsorption function, a substance surface high-speed cleaning function and an antiseptic function, so that it becomes possible to clean various substances with high performance and low environmental load so as to purify contaminated water.
As yet another prior art, JP 2003-334548A has disclosed a nanobubble generation method.
In the nanobubble generation method according to this prior art, there is provided with (1) a step for gasifying part of liquid by decomposition in liquids, (2) a step for applying ultrasonic waves in liquids, or (3) a step for gasifying part of liquid by decomposition and a step for applying ultrasonic waves.
Both these two prior arts have disclosed purification of contaminated water by using nanobubbles or removal of dirt on the surface of solids by using nanobubbles. However, the two prior arts fail to disclose any technology for enhancing efficiency in treatment and quality of treated water by increasing the activity of microorganisms when treating wastewater containing organic matter with use of microorganisms.